Investigating Citric Acid Cycle Perturbations in Complex I Deficient Mitochondrial Encephalopathy

摘要 线粒体疾病是呼吸链疾病，线粒体不再在其中运行 有效地产生三磷酸腺苷，通常是由于氧化的一个或多个成分出现问题 磷酸化机器。表现为脑病的线粒体疾病的发生率为1/5000 活产，通常在生命的头几年是致命的。这些疾病的遗传原因和临床过程 脑病，如复杂I缺乏症，是很好的描述。对这些疾病的有效治疗 疾病受到我们对驱动神经元衰退的病理机制缺乏机械性理解的限制， 超越了已知的复合体-I生物能量赤字。 我们之前已经描述了柠檬酸循环代谢产物富马酸与蛋白质半胱氨酸的反应。 残基产生不可逆的修饰，2-琥珀酸半胱氨酸(2SC)，也称为蛋白质琥珀酸化。 线粒体复合体I的Ndufs4基因敲除小鼠模型中富马酸和蛋白质琥珀酸化增加 缺乏症。我们证明了α-酮戊二酸脱氢酶(α-)的一个成分的琥珀酸化。 KGDH)复合体会削弱该复合体的酶活性。这导致琥珀酰辅酶A产生减少， 并损害底物水平的磷酸化，以产生急需的GTP/ATP。我们假设新陈代谢 复合体I丢失引起的酸中毒使α-KG重定向生成2-羟基戊二酸。我们预测 这会影响受影响神经元的表观遗传格局。 在Ndufs4基因敲除小鼠中，其他非神经细胞的柠檬酸循环也受到影响。我们展示了 初步数据显示产生衣康酸的能力受损，衣康酸是一种重要的抗炎药物 代谢物。考虑到小胶质细胞聚集在神经病理损伤的中心，这一点很明显。我们的 新的假说将特定的柠檬酸循环扰动与蛋白质的化学修饰联系起来，这可能 在受病理影响最严重的区域加速生化破坏。要解决这些具体问题 病理机制我们概述了针对性的治疗方法，应该减少神经病理的驱动因素。

ABSTRACT Mitochondrial diseases are respiratory chain disorders in which the mitochondria are no longer operating efficiently to produce ATP, usually due to a problem with one or more components of the oxidative phosphorylation machinery. Mitochondrial diseases manifesting as encephalopathies occur at a rate of 1 in 5000 live births and are often fatal in the first few years of life. The genetic cause and clinical course of these encephalopathies, e.g., Complex I deficient Leigh Syndrome, are well-described. The effective treatment of these diseases is limited by our lack of mechanistic understanding of pathomechanisms that drive neuronal decline, beyond the known Complex-I bioenergetic deficit. We have previously described the reaction of the citric acid cycle metabolite fumarate with protein cysteine residues to generate an irreversible modification, 2-succinocysteine (2SC), also known as protein succination. Fumarate and protein succination increase in the Ndufs4 knockout mouse model of mitochondrial Complex I deficiency. We demonstrate that the succination of a component of the α-ketoglutarate dehydrogenase (α- KGDH) complex impairs the enzymatic activity of this complex. This results in decreased succinyl CoA production, and impaired substrate level phosphorylation to produce much needed GTP/ATP. We hypothesize that metabolic acidosis derived from the Complex I loss redirects α-KG toward 2-hydroxyglutarate production. We predict that this influences the epigenetic landscape in the affected neurons. The citric acid cycle of other non-neuronal cells are also impacted in the Ndufs4 knockout mouse. We show preliminary data to demonstrate an impaired ability to produce itaconate, an important anti-inflammatory metabolite. This is significant given the accumulation of microglia in the center of neuropathological lesions. Our novel hypotheses link specific citric acid cycle perturbations to the chemical modifications of proteins that may accelerate the biochemical damage within the regions most affected by pathology. To address these specific pathomechanisms we outline targeted therapeutic approaches that should reduce the drivers of neuropathology.